If you’ve ever spent the night tossing and turning because your bedroom is too hot, you likely know all too well how important temperature is for ensuring you sleep well. However, have you ever stopped to wonder why our body is so sensitive to temperature while sleeping? It has less to do with your environment’s temperature and more to do with your body temperature.
Sleep and temperature have a bidirectional relationship, meaning your body temperature can affect your sleep, and your sleep cycles/circadian rhythm cause changes in your body temperature. Understanding this relationship is crucial for ensuring you can sleep more easily through the night, especially since temperature is an element of good sleep hygiene.
How Your Circadian Rhythm Modulates Your Temperature
There’s a reason why your room, which had been a comfortable temperature all day, becomes too hot at night, even when you kick off the blankets.
We’ve been told that a normal body temperature is 37ºC (98.6ºF), but our body temperature fluctuates throughout the day by as much as 0.5ºC (0.9ºF). These changes are dictated by our circadian rhythm, the 24-hour internal clock that dictates our sleep-wake cycles.
Our body temperature starts the day on the lower end of the scale, then increases when we wake up, only to drop down again when we go to sleep. This quick drop in body temperature, seen at night across all mammals, is believed to signal to the body that it is time to prepare for sleep.
As the night progresses, your body temperature remains low. In fact, any increases in temperature have been shown to promote waking—this correlates with findings that, around four a.m., your core body temperature starts to rise and continues rising during the day. So, if your body temperature increases during the night, your brain may mistakenly believe that it is morning, leading to a nighttime waking.
This connection between circadian rhythm and temperature may also explain some sleep disorders. For instance, those with insomnia have been shown to have core body temperature fluctuations that are out of sync with normal rhythms. Essentially, their body temperature does not lower at their chosen bedtime, which contributes to their difficulty sleeping.
The body’s process of thermoregulation is also linked to various sleep-promoting processes.
Our skin is rich in arteriovenous anastomoses, which influence blood flow to the skin. An increased skin temperature is largely due to a greater flow of heated blood, which is done to facilitate heat loss to the environment. This increased blood flow helps to promote the rapid onset of sleep and is also associated with melatonin secretion, with melatonin being your body’s sleepiness hormone.
Research has found that increasing melatonin can decrease core body temperature by having blood vessels open up to release heat, so it may be your melatonin production that helps to lower your body temperature in preparation for bedtime. Thus, if you do not produce enough melatonin, such as if you’re going to bed before your circadian rhythm is ready, you may find that your body temperature has not lowered yet to a point that promotes sleepiness.
How Temperature Affects Your Sleep
Research has shown that the temperature of our environment is a key determinant of sleep due to the strong link between thermoregulation and the mechanism regulating sleep. Both temperatures that are too high or too low can affect your sleep even if you don’t typically struggle with insomnia.
As for why environmental temperature is so influential on our sleep, it has to do with the discrepancy between our body temperature and the temperature of our bedroom.
As we know, our body temperature lowers leading up to sleep, and these changes in body temperature make you more sensitive to the temperature of your environment—when your body temperature decreases, the outside temperature feels as though it is higher, which can then create feelings of discomfort. As such, at night, the temperature in our environment needs to lower, as well, to match the changes in our body temperature.
There are also changes in your temperature throughout the night, in tune with the sleep stages; your body cools as it enters NREM sleep and then rises slightly in REM sleep. This means that your deep sleep, which occurs during the NREM stage, can be even more sensitive to temperature since your body temperature is naturally lower during this stage.
With disturbed sleep being a contributor to health conditions such as obesity, quality of life, and mortality, keeping your bedroom and body temperature within an ideal range is crucial for your health and well-being.
Cool Down to Sleep Better
If you’re looking to improve your sleep, make sure that your room and body are cool enough to prompt restful sleep.
Lower Your Room Temperature
If you’re too hot at night, it may be worthwhile to ensure your room is cool enough. That’s not to say that you should drop your room’s temperature to the lowest setting, though—if you’re too cold, you may struggle to sleep as well.
Instead, take the time to find your comfort level, taking into consideration your bedding. You should be able to lie under them comfortably to create a temperature gradient where you’re warm under the covers, but the cooler bedroom temperature allows your body to release heat through the head and any exposed hands or feet.
Take A Warm Bath
It may seem counterintuitive, but taking a warm bath or shower before bed can help lower your body temperature, helping you fall asleep faster, sleep longer, and get more deep sleep.
This is because taking a bath and warming your body helps your blood vessels dilate, which then leads to significant heat loss, similar to what your body achieves before bed. Taking a warm bath essentially kicks this element of your night into motion and can be helpful if your body is off tune.
Fine Tune Your Bedding
The bedding that you opt for can make or break your night. If you’re often hot, consider something thinner, while if you’re usually shivering, opt for a thicker blanket.
A good option is to use layers on your bed so that you can add and remove them as needed to reach your ideal comfort level.
Using Temperature to Sleep Better
Your circadian rhythm dictates natural fluctuations in your body temperature that correlate with your sleep-wake cycle—your body temperature lowers at night and rises come morning. This means that temperature is crucial for ensuring your body knows to prepare for sleep and remains asleep during the night.
Initiating habits that keep your body temperature from rising, and even promote a rapid decline before bed, can help you fall asleep more easily and wake up in the morning more rested.
